In 1879, the geologist Otto Hahn announced the discovery of
(fossilised) extraterrestrial life in meteorites.

Bioastronomy, though not yet named, was a booming field of
research in the 1860s and '70s. The best-selling science writer
Camille Flammarion brought out
La Pluralité des Mondes Habités in 1864, making
alien life an acceptable topic of polite conversation. In 1871 Sir William
Thomson (Lord Kelvin), undisputed leader of the physics community's opposition
to Darwinian evolution, created a sensation by proposing that life
passed endlessly from world to world in the eternal universe: as an old
planet crumbled, its remains became life-bearing meteorites, "moss-grown
fragments from the ruins of another world," seeding a younger planet
elsewhere.(The same idea had already been proposed independently by
the Dresden botanist Hermann Eberhard Richter.)
Biologists, for the most part, were scandalised, but the great Helmholtz came out
as a supporter of the Richter-Thomson theory, suggesting mechanisms by which
bacteria on rocks could survive interplanetary voyages.

That meteorites, or at least
carbonaceous chondrites, are rich in organic material had been known since the
1830s; the possibility that they exhibit biological activity had been considered (and rejected)
by Berzelius in 1834. In 1868 Berthelot suggested a reaction between
metal carbides and water as an abiotic source for the petroleum-like substances in
meteorites, but not everyone was convinced; some chondrites seemed so very
coal-like that it was difficult to believe they were not formed in the same way
that coal was. This was the backdrop of Hahn's announcement.

Hahn is sometimes derisively called an "amateur" in modern works, but this is
misleading. He had a Ph.D. in geology, and, although it is true that he worked as a
lawyer rather than as an academic, this was hardly uncommon in the Nineteenth
Century. His laboratory technique was entirely professional, and he was one
of the first mineralogists to photograph transparently-thin cross-sections of rock
samples, later a standard method. It was the way he interpreted his results
which generated controversy.

Hahn's first book Die Urzelle (1879) announced the discovery of alga-like plant fossils in
the 1866
Knyahinya chondrite and, even more surprisingly, in the 1776 Toluca iron.
He believed these organisms were akin to Eozoön, the fossil
microbe discovered in 1865 by J. W. Dawson in Precambrian
Canadian limestone and claimed to be the oldest known form of life.

The following year, in Die Meteorite und ihre Organismen, Hahn
reported examining twenty meteorites, none of them carbonaceous, and
finding not only microbes but also corals and crinoids. He described a
new sponge genus, Urania, named for the muse of astronomy. The only
question still unresolved in his mind was whether these were indeed
specimens of extraterrestrial
life, or whether meteorites might be pieces of terrestrial rock somehow
hurled into space. The former hypothesis struck him as more likely.

By 1881, Hahn's findings were attracting global attention. Hahn corresponded
with Charles Darwin, suggesting that evolutionists should welcome rather
than oppose panspermia, as it enabled them to dodge the problems associated
with the ultimate origin of life without threatening their views on its subsequent
development. (Accounts of Darwin's response vary.)
A
synopsis of Hahn's research in Popular Science declared:

"The great problem, whether or not other celestial bodies besides our own planet
are or in past ages have been inhabited by animate beings, must be a subject of the
deepest interest to every thinking being. This question has for some time past been
answered in the affirmative with great probability ... But now at last it seems that we
have obtained a direct answer to this question, and that we are able to see with our
own eyes the veritable remains of animate beings from another celestial body."

With our own eyes: it was the superb photographs which were Hahn's strongest
evidence. They plainly showed complex, seemingly biological structures. The only
difficulty was an embarassment of riches; the "fossils" were ubiquitous. On this the
critics immediately pounced. The geologist Stanislas-Étienne Meunier
brought a tube of porcelain to red heat and prepared sections.
He found "fossils" just like Hahn's: crinoids, seemingly. But clearly they were
artefacts, not present before the tube was heated.

The tide turned. In 1882 Carl Vogt wrote Les Prétendus Organismes
des Meteorites, with
cross-section images even more beautiful than Hahn's, but the
structures visible in the plates were now clearly recognised as pseudofossils.
By the 1890s, Eozoön had met the same fate.

But history repeats itself. Svante Arrhenius revived and improved the Richter-Thomson
panspermia theory in 1907; the cosmologist Fred Hoyle and his associates would
champion it throughout the second half of the Twentieth Century. In the 1920s, C. B.
Lipman would claim to have isolated live microbes in stony meteorites
(and in ancient terrestrial rocks), but his results would be attributed to contamination.
B. Nagy would discover fossils in meteorites in the 1960s, starting a furious controversy
which would be eclipsed by that over microbial remains allegedly seen in the Martian-origin
meteorite ALH84001 in 1996; in both cases, the consensus of the scientific community would be
"pseudofossils".